Common x-ray tubes generate x-rays by hitting electrons against a metal anode target with high energy. For example, an x-ray tube uses a principle of generating Bremstralung x-rays or specific x-rays generated, depending on the substance of the anode target. The electron source that emits electrons is usually a thermal electron source.
Meanwhile, there is an x-ray tube emitting electrons by using nano-substances. The x-ray tube uses a field emitter. It is important in the x-ray tube using a field emitter to apply nano-substances, which are effective for field emission, to a cathode electrode, to form a gate electrode to apply an electric field to the nano-substance, and to seal the structure of the x-ray tube under vacuum.
The x-ray tube using the field emitter decreases in degree of vacuum due to gases exhausted from the inner wall or the field emitter even after the x-ray tube is sealed under vacuum. In order to maintain the degree of vacuum, a getter is disposed in the x-ray tube to maintain the vacuum.
However, there is a problem in that the getter cannot be activated because the getter is mounted in the sealed x-ray tube. That is, it is difficult to activate the getter at the point of time of when the degree of vacuum in the sealed x-ray under vacuum tube decreases.